Porcine circovirus type 3 (PCV3) is a newly discovered pathogen that causes porcine
dermatitis and nephropathy syndrome (PDNS)-like clinical signs, multisystemic
inflammation, and reproductive failure.
Heme oxygenase-1 (HO-1), a stress-inducible
enzyme, exerts protective functions by converting
heme into
carbon monoxide (CO),
biliverdin (BV), and
iron. However, the effects of HO-1 and its metabolites on PCV3 replication remain unknown. In this study, experiments involving specific inhibitors, lentivirus transduction, and
small interfering RNA (
siRNA) transfection revealed that active PCV3
infection reduced HO-1 expression and that the expression of HO-1 negatively regulated virus replication in cultured cells, depending on its enzymatic activity. Subsequently, the effects of the HO-1 metabolites (CO, BV, and
iron) on PCV3
infection were investigated. The CO inducers (
cobalt protoporphyrin IX [CoPP] or tricarbonyl dichloro
ruthenium [II] dimer [CORM-2]) mediate PCV3 inhibition by generating CO, and this inhibition is reversed by
hemoglobin (Hb; a CO scavenger). The inhibition of PCV3 replication by BV depended on BV-mediated
reactive oxygen species (ROS) reduction, as
N-acetyl-l-cysteine affected PCV3 replication while reducing ROS production. The reduction product of BV,
bilirubin (BR), specifically promoted
nitric oxide (NO) generation and further activated the
cyclic GMP/
protein kinase G (cGMP/PKG) pathway to attenuate PCV3
infection. Both the
iron provided by FeCl3 and the
iron chelated by
deferoxamine (DFO) with CoPP treatment failed to affect PCV3 replication. Our data demonstrate that the HO-1-CO-cGMP/PKG, HO-1-BV-ROS, and HO-1-BV-BR-NO-cGMP/PKG pathways contribute crucially to the inhibition of PCV3 replication. These results provide important insights regarding preventing and controlling PCV3
infection. IMPORTANCE The regulation of host
protein expression by
virus infection is the key to facilitating self-replication. As an important emerging pathogen of swine, clarification of the interaction between PCV3
infection and the host enables us to understand the viral life cycle and pathogenesis better.
Heme oxygenase-1 (HO-1) and its metabolites
carbon monoxide (CO),
biliverdin (BV), and
iron have been demonstrated to involve a wealth of viral replications. Here, we, for the first time, demonstrated that HO-1 expression decreases in PCV3-infected cells and negatively regulates PCV3 replication and that the HO-1 metabolic products CO and BV inhibit PCV3 replication by the CO- or BV/BR/NO-dependent cGMP/PKG pathway or BV-mediated ROS reduction, but the
iron (the third metabolic product) does not. Specifically, PCV3
infection maintains normal proliferation by downregulating HO-1 expression. These findings clarify the mechanism by which HO-1 modulates PCV3 replication in cells and provide important targets for preventing and controlling PCV3
infection.